1. Field of the Invention
The present invention relates generally to a method of detecting a physical downlink control channel (PDCCH) in a long-term evolution (LTE) system and, more particularly, to a method of detecting a PDCCH in an LTE system that is capable of reducing computational load that is required to detect downlink control information (DCI) from a PDCCH allocated to a common space when detecting the DCI at a receiving end, thereby enabling overall DCI to be rapidly detected.
2. Description of the Related Art
In an LTE system, downlink signals may be classified into a PDCCH and a data signal. User equipment (UE) receives downlink signals from a base station, and then uses DCI, obtained by decoding a PDCCH, to detect a data signal or to control uplink transmission.
FIG. 1 is a diagram illustrating the structure of the PDCCH and data signal of LTE downlink signals. As illustrated in FIG. 1, the PDCCH and the data signal are located in different regions in terms of time within a sub-frame, that is, the transmission time interval (TTI) of downlink signals.
FIG. 2 is a block diagram illustrating a process in which DCI in a binary number form is modulated into a PDCCH in a complex number form within LTE downlink signals. As illustrated in FIG. 2, DCI used in the LTE system standard is converted into a PDCCH through encoding, scrambling and symbol mapping, is allocated to a resource in the control region of a sub-frame, and is then transmitted.
In detail, a plurality of pieces of DCI may be multiplexed into a single signal and then transmitted. The reason for this is that a single piece of DCI can control only a single function in an LTE system. That is, to control various functions through a single downlink signal transmission, a plurality of pieces of DCI should be transmitted at the same time. The types of DCI of the LTE system and the functions that are controlled by the types of DCI are summarized in the following Table 1:
TABLE 1DCI formatFunctionDCI 1, DCI 1A, DCI 1B, DCI 1C, DCIdownlink data signal detection1D, DCI 2, DCI 2A, DCI 2B, DCI 2CinformationDCI 0, DCI 3, DCI 3A, DCI 4uplink data signal transmissioncontrol informationDCI 1Auplink random access procedureinformation
Meanwhile, to detect a downlink data signal, DCI in a unique format is used in accordance with the transmission technique that is used to transmit the data signal. When uplink data signal transmission is controlled, DCI in a unique format is used in accordance with the technique that transmits an uplink data signal, and DCI indicative of uplink transmission power information is distinguished by a unique format. Downlink data signals are also distinguished by their various purposes. Accordingly, information is additionally required to distinguish the purposes of downlink data signals. In the LTE system, a radio network temporary identifier (RNTI) of 16 bits is defined, and used to distinguish the purposes of data signals. In the LTE system, the types and purposes of RNTIs are summarized in the following Table 2:
TABLE 2Type of RNTIPurposeP-RNTIpaging, checking of variations insystem informationSI-RNTIbroadcast transmission of systeminformationM-RNTIchecking of variations in MCCHinformationRA-RNTItransmission of response of randomaccessTemporary C-RNTIcontention resolution, Msg3transmissionC-RNTIdynamically scheduled unicasttransmissionSPS C-RNTIsemi-persistently scheduled unicasttransmissionTPC-PUCCH-RNTIphysical layer power controlTPC-PUSCH-RNTIphysical layer power control
According to the above Table 2, the DCI of a specific function is determined based on DCI format information and RNTI information. All of the possible combinations of DCI format information and RNTI information that determine DCI are summarized in the following Table 3:
TABLE 3DCI formatType of RNTI to be combinedDCI 0, 1C-RNTI, SPS C-RNTI, Temporary C-RNTIDCI 1ASI-RNTI, P-RNTI, RA-RNTI, C-RNTI,SPS C-RNTI, Temporary C-RNTIDCI 1B, 1DC-RNTIDCI 1CSI-RNTI, P-RNTI, RA-RNTI, M-RNTIDCI 2, 2A, 2B,C-RNTI, SPS C-RNTI2CDCI 3/3ATPC-PUCCH-RNTI, TPC-PUSCH-RNTIDCI 4C-RNTI
Once the DCI format has been determined as described above, the DCI of the determined format is formed, and then 16-bit Cyclic Redundancy Check (CRC) information (hereinafter referred to as “pure CRC information”), obtained using the CRC pattern of the LTE standard in the form of a 16-th polynomial, is affixed to the rear end of DCI in order to detect errors prior to encoding. RNTI information is included by performing an XOR operation on the 16-bit pure CRC information added at the process of affixing CRC information and 16-bit RNTI information (hereinafter a portion in which the RNTI information has been included in the pure CRC information is referred to as the “CRC information including an RNTI”). After the process of affixing the pure CRC information and the RNTI information to each other has been completed, convolutional encoding is performed. During rate matching that is performed after the encoding, the DCI is deformed to a PDCCH, in which case the output length is determined by PDCCH format information. Such PDCCH format information is listed in the following Table 4:
TABLE 4PDCCH FormatsNumber of PDCCH Bits072114422883576
Thereafter, a PDCCH is generated using the DCI determined based on the DCI format, the DCI, the RNTI information and the PDCCH format information. The PDCCH in a binary number form, generated through the above process, is converted into a complex number form through scrambling and symbol mapping, is allocated to a resource within a sub-frame, and is then transmitted.
Meanwhile, a PDCCH including DCI that is used in common by all UEs within the coverage area of a base station is allocated to a resource region defined as a common space, and a PDCCH including DCI that is used only by specific UE is allocated to a resource region defined as a UE-specific space. The PDCCHs that may be allocated to common and UE-specific spaces may be distinguished based on RNTI, as shown in the following Table 5:
TABLE 5Resource AllocatedRegionRNTIPDCCH Size (bits)Common spaceSI-RNTI, P-RNTI, RA-RNTI,72, 144, 288, 576C-RNTI, SPS C-RNTI, M-RNTI, Temporary C-RNTI,TPC-PUCCH-RNTI,TPC-PUSCH-RNTIUE-specific spaceC-RNTI, SPS C-RNTI,288, 576Temporary C-RNTI
When physical downlink control channels (PDCCHs) are allocated to the common space, the common space is allocated sequentially from the front of a control region. In contrast, when PDCCHs are allocated to the UE-specific space, an allocated location varies depending on selected RNTI information and a current sub-frame number.
Meanwhile, the UE receives base station signals, detects a PDCCH therefrom, and decodes DCI based on the PDCCH. In the process of detecting the PDCCH, the UE cannot be aware of the location of a resource to which the PDCCH has been allocated, and cannot be aware of the PDCCH format, that is, the size of the PDCCH, at the allocated location. In this situation, to correctly detect the PDCCH transmitted by the base station, the UE should find the location of the control region to which the PDCCH transmitted by the base station has been allocated, and the size of the PDCCH.
The UE attempts to detect the signal while taking into consideration all combinations of information about the location to which the PDCCH has been allocated, the DCI format information, the RNTI type and the PDCCH format information in the state in which the UE cannot be aware of the four types of information. Meanwhile, the PDCCH formats that can be allocated to the common space and the UE-specific space, that is, resource Allocated Regions, and the number of PDCCH formats have been determined, and are shown in the following Table 6:
TABLE 6Type of AllocatedNumber of PDCCHs thatRegionPDCCH Formats (bits)can be allocatedUE-specific space0 (72) 61 (144)62 (288)23 (576)2Common space2 (288)43 (576)2
Referring to Tables 3, 5 and 6 in a collective manner, the DCI formats, the RNTI types, the PDCCH formats and the number of PDCCH formats that can be allocated for specific resource allocation can be found. For example, according to Table 3, DCI format 1A may form a PDCCH in combination with a P-RNTI. According to Table 5, a PDCCH including a P-RNTI is allocated to the common space. Finally, according to Table 6, PDCCHs allocated to the common space may have PDCCH formats 2 and 3, and PDCCHs whose number is defined for each format may be allocated.
Based on the above description, the base station transmits a PDCCH based on a specific combination of a DCI format, an RNTI type, a PDCCH format and a resource Allocated Region. The UE receives this signal, and attempts to detect a signal with respect to all possible combinations of the PDCCH. If the signal is detected based on a specific combination and the results of decoding are determined to have no error after a CRC, it is determined that DCI related to the combination has been transmitted, and the decoded binary signal is used as the DCI.
The combinations that the UE should take into consideration to detect a PDCCH may be summarized in the following Table 7:
TABLE 7PDCCH formats(maximumnumber ofAllocatedallocatedregionDCI FormatType of RNTI to be combinedformats)CommonDCI 1C-RNTI, Temporary C-RNTI, SPS C-2 (4)spaceRNTI3 (2)DCI 1ASI-RNTI, P-RNTI, RA-RNTI, C-RNTI,SPS C-RNTI, Temporary C-RNTIDCI 1CSI-RNTI, P-RNTI, RA-RNTI, M-RNTIDCI 3TPC-PUCCH-RNTI, TPC-PUSCH-RNTIDCI 3ATPC-PUCCH-RNTI, TPC-PUSCH-RNTIUE-DCI 0C-RNTI, SPS C-RNTI0 (6)specificDCI 1C-RNTI, SPS C-RNTI, Temporary C-1 (6)spaceRNTI2 (2)DCI 1AC-RNTI, SPS C-RNTI, Temporary C-3 (2)RNTIDCI 1BC-RNTIDCI 1DC-RNTIDCI 2C-RNTI, SPS C-RNTIDCI 2AC-RNTI, SPS C-RNTIDCI 2BC-RNTI, SPS C-RNTIDCI 2CC-RNTI, SPS C-RNTIDCI 4C-RNTI
When PDCCHs are assigned to the common space, the common space is assigned sequentially from the front of a control region. For example, when PDCCH1 including DCI format 1C, a P-RNTI and PDCCH format 2 and PDCCH2 including DCI format 1A, a C-RNTI and PDCCH format 2 are allocated to the common space, PDCCH1 is allocated to a region extending from the front of a control region by the length of PDCCH format 2, and then PDCCH2 is allocated subsequently. FIG. 3 is a block diagram illustrating a process in which PDCCHs are assigned to the common space.
In contrast, when PDCCHs are assigned to the UE-specific space, a location allocated an RNTI value varies. That is, when a plurality of PDCCHs including different RNTIs are allocated, the plurality of PDCCHs is not sequentially allocated because of allocated locations that are determined depending on the RNTIs.
In this process, the UE receives signals from the base station, and detects a PDCCH. In this case, the UE cannot find Allocated Region information, DCI format information, RNTI information and PDCCH format information with the PDCCH that is generated by the base station. Accordingly, the UE detects the PDCCH through the following process.
FIG. 4 is a diagram illustrating a process of attempting a PDCCH in the common space. In FIG. 4, PDCCHs, in each of which possible DCI formats and RNTI information are combined, may be located at the locations of PDCCH1 to PDCCH6. Since 17 combinations of DCI formats and RNTIs are possible for the common space in accordance with Table 7 and six CRCs are required for each of the combinations, as illustrated in FIG. 4, a total of 102 CRCs should be performed for the UE to detect the PDCCH in the common space.
FIG. 5 is a flowchart illustrating a conventional method of detecting a PDCCH in an LTE system. As illustrated in FIG. 5, in accordance with the conventional method of detecting a PDCCH in an LTE system, first, base station signals are received at step S10, in which case it is assumed that a PDCCH has been allocated to a common space.
In this state, at step S15, one is selected from among possible PDCCH formats, and a signal corresponding to the length of the selected PDCCH format is retrieved from the common space.
Thereafter, at step S20, one is selected from among possible DCI formats, and at step S25, decoding is performed using the signal retrieved at step S15 and the DCI format information selected at step S20. Thereafter, at step S30, one is selected from among possible pieces of RNTI information, and at step S35, a CRC is performed after the RNTI information has been eliminated from CRC information including an RNTI. In a CRC process, when the signal that has undergone decoding and RNTI information elimination is divided by a CRC pattern, the decoding is determined to be successful if the remainder is 0, and the decoding is determined to fail if the remainder is not 0.
Thereafter, at step S40, it is determined whether the decoding is successful. If the decoding is successful, these pieces of information, that is, the DCI obtained when the decoding is successful and the DCI format and the RNTI information at the time, are stored at step S75 and then step S45 is performed in order to perform a control function corresponding to the corresponding combination of the DCI format and the RNTI information. In contrast, if the decoding is not successful, step S45 is immediately performed without the storage of any information. At step S45, it is determined whether all of the RNTIs have been selected. If, as a result of the determination at step S45, not all of the RNTIs have been selected, the process proceeds to step S50, where one is selected from among one or more RNTIs that have not been selected yet, and then returns to step S35. In contrast, if all of the RNTIs have been selected, the process proceeds to step S55, where all of the DCI formats have been selected.
If, as a result of the determination at step S55, not all of the DCI formats have been selected, the process proceeds to step S50, where one is selected from among one or more DCI formats that have not been selected yet, and then returns to step S25. In contrast, if all of the DCI formats have been selected, the process proceeds to step S65, where it is determined whether all of the PDCCH formats have been selected.
If, as a result of the determination at step S65, all of the PDCCH formats have been selected, the process ends. In contrast, if not all of the PDCCH formats have been selected, the process proceeds to step S70, where one is selected from among one or more PDCCH formats that have not been selected yet and a signal corresponding to the length of the selected PDCCH format is retrieved, and then returns to step S20.
After the PDCCH has been detected in the common space as described above, it is assumed that a PDCCH has been allocated to the UE-specific space, and the above-described process of FIG. 5 is performed. Unlike in the case of UE-specific space allocation in which a location to which a PDCCH is allocated is variable because of an RNTI value, allocation is performed sequentially from the front of the space in common space allocation.
In accordance with Table 7, in the common space, DCI format 0 may be combined with three types of RNTI information, DCI format 1A may be combined with six types of RNTI information, and DCI format 1C may be combined with four types of RNTI information. In the same manner, DCI format 3 may be combined with two types RNTI information, and DCI format 3A may be combined with two types of RNTI information. Accordingly, since a total of 17 combinations of DCI formats and RNTIs are possible and six CRCs are performed for each of the combinations, as illustrated in FIG. 4, a total of 102 (=17×6) CRCs, that is, an excessive number of tests, are required. Accordingly, the conventional method has the problems of an excessive amount of computational load and an excessively long test time.